Method for making a mosaic of ultrasonic transducers adapted for use with image conversion tubes

ABSTRACT

A mosaic of ultrasonic transducers is assembled and manufactured and adapted to the faceplate of an image conversion tube in a simple and expeditious procedure: a layer of piezoelectric material is joined to a layer of conductive syntactic foam preferably this is accomplished with a conductive epoxy material. The remaining side of the syntactic foam layer is then joined, suitably with conductive epoxy adhesive material, to the wire fiber optic faceplate of an image conversion tube. A plurality of spaced parallel slots are formed through the two layers of material and to a depth just into the tube faceplate, and a plurality of spaced parallel slots are formed perpendicular to the aforementioned slots in the piezoelectric and foam layers also to a depth just into the tube faceplate. The resulting configuration is a checkerboard mosaic of piezoelectric transducers which are spaced from each other, acoustically isolated from one another, and electrically coupled to individual wires in the tube faceplate. A novel result of this process permits substitution of other transducers to the faceplate of a conversion tube by simply scrapping off the old transducer and reforming the new mosaic on the tube faceplate in the same manner as described.

United States Patent [54] METHOD FOR MAKING A MOSAIC OF ULTRASONIC TRANSDUCERS ADAPTED FOR USE WITH IMAGE CONVERSION TUBES 4 Claims, 6 Drawing Figs.

[52] [1.8. CI 29/25.35 [S1 Int. Cl B01j 17/00, H04r 17/00 [50] Field of Search 29/2535,

[56] References Cited UNITED STATES PATENTS 3,515,910 6/1970 Fritz et al...... 340/10 3,325,777 6/1967 Fyler 340/3 Primary Examiner-1ohn F. Campbell Assistant Examiner-D. M. Heist Attorneys-Alan C. Rose, Alfred B. Levine, Ronald W. Reagin and Ronald M. Goldman ABSTRACT: A mosaic of ultrasonic transducers is assembled and manufactured and adapted to the faceplate of an image conversion tube in a simple and expeditious procedure: a layer of piezoelectric material is joined to a layer of conductive syntactic foam preferably this is accomplished with a conductive epoxy material. The remaining side of the syntactic foam layer is then joined, suitably with conductive epoxy adhesive material, to the wire fiber optic faceplate of an image conversion tube. A plurality of spaced parallel slots are formed through theltwo layers of material and to a depth just into the tube faceplate, and a plurality of spaced parallel slots are formed perpendicular to the aforementioned slots in the piezoelectric and foam layers also to a depth just into the tube faceplate. The resulting configuration is a checkerboard mosaic of piezoelectric transducers which are spaced from each other, acoustically isolated from one another, and electrically coupled to individual wires in the tube faceplate. A novel result of this process permits substitution of other trans ducers to the faceplate of a conversion tube by simply scrapping off the old transducer and reforming the new mosaic on the tube faceplate in the same manner as described.

transducer mosaic and, more particularly, to the method of lo manufacture and assembly of an. image conversion tube which utilizes a mosaic of ultrasonic transducers.

image conversion systems are used to provide a visible display of visible and particularly invisible field patterns. Aptly defined as the description of the physical properties of a given region, the field patterns may be formed of electromagnetic energy, such as light, compressional wave energy, such as ultrasonic energy, atomic energy, such as X-ray particles, infrared, electric field and magnetic field. One particular system which has undergone extensive investigation in recent years is. the image conversion system for underwater viewing.

In the latter system an object submerged in water is illu minated with ultrasonic energy and ultrasonic field pattern reflected from the object is detected with suitable apparatus and the detected signals are converted and displayed as a. corresponding visible image. Vital to such a system is the image conversion tube which incorporates or has associated therewith acoustic-to-voltage transducers of suitable resolution to convert the field of ultrasonic energy into a corresponding field of electrical signals.

ln the Hydrocon image conversion system described inv U.S. Pat. No. 3,325,777 a mosaic of ultrasonic transducers is employed. Each transducer is connected through its own circuit. including amplifier detectors, etc. to the wire fiber electronics faceplate of an image conversion tube. The tube faceplate is a ceramic plate, an insulator, penetrated by many small wires so that any externally impressed, voltages applied to the wires by the corresponding transducer appears at the end of the wire fiber internal of the tube. The voltage field so formed is read" by an electron beam within the tube that scans allthe wires. Thereafter this infonnation is processed and coupled to a conventional display apparatus. As is apparent the resolution available in this system is limited by the density of wires in the faceplate, the size of the transducer, and the number of transducers in the mosaic.

This requirement is found also in the improved mosaic structure disclosed in my copending application entitled Mosaic Transducer for lmaging'Tubes, Ser. No. 809,683, filed Mar. 24, 1969 in which the ultrasonic transducers are arranged in a mosaic and attached through a corresponding mosaic of coupling means or pressure release barrier comprising a conductive syntactic foam to the wire fiber optic faceplate. As the size of the transducer is lessened in order to permit the attachment of a larger number of transducers in a small mosaic it would appear exceedingly difficult and tedious for the mosaic transducer structure found in either the hydrocon system or that described in my cited copending application to independently mount and space each of the transducers in the mosaic to the circuitry and to the faceplate.

Accordingly, it is an object of this invention to provide a novel method for constructing a transducer mosaic;

It is a further object of the invention to provide a method of manufacturing an ultrasonic transducer mosaic that is simple and expeditious; and,

It is a still further object of the invention to provide a novel method of manufacturing a mosaic of transducers which does not require the individual assembly of single parts thereof in a one-at-a-time manner.

ln accordance with the invention a transducer mosaic is assembled or an image conversion tube in the steps of joining together a layer of transducer material, suitably piezoelectric, with a layer of a conductive syntactic foam which comprises a mixture of minute hollow glass balls and conductive epoxy resin and then joining the free surface of the foam layer in turn to the wire fiber electronics faceplate of the image conversion tube with a suitable adhesive such as the conductive epoxy material. Subsequently with the use of a suitable saw a plurality of slots are sliced, both horizontal and vertical, through the attached layers. Preferably these slots are cut through the attached layers to a depth which just penetrates the fiber electronics faceplate to form the mosaic of electrically insulated and substantially acoustically isolated ultrasonic transducers.

The foregoing and other objects of the invention together with other advantages and features believed to be characteristic of the novel method are better understood from the following detailed description taken together with the figures of the drawings in which:

FIG. 1 illustrates schematically an image conversion tube having a mosaic constructed in accordance with the invention;

H08. 20, 2b, and 2c illustrate the steps used tov construct the transducer mosaic;

FIG. 3 illustrates schematically in cross section a side view of the upper portion of an image conversion tube; and,

H6. 4 illustrates schematically in cross section similar to that of FIG. 3 for an alternative image conversion tube.

FIG. 1 schematically illustrates the complete image conversion tube which includes the transducer mosaic l, fiber optics faceplate 2, and the tube body 3. The tube body 3 includes conventional elements, not illustrated, of a pickup device such as the vidicon or orthicon and includes a source ofelectronsfor forminga beam which is used to scan the faceplate and is conventional. Reference may be made to U.S. Pat. No. 3,325,777 and to the literature for greater details. Fiber optics faceplate- 2 is represented by the dashed lines as exemplary sinceit forms the end of the imaging tube body. The faceplate includes a matrix of very fine wires 4 extending therethrough from top tobottom. These wires are insulated from one another by the glass or ceramic material of the faceplate.

Mosaic 1 is attachedto and supported by faceplate 2. Mosaic 1 consists of a plurality of insulated piezoelectric elements 5 in the form of a thin slab. The piezoelectric slab is attached to and supported by a pressure release material 6 which in turn is attached. to and supported by faceplate 2. For purposes of joining theelements as described a suitable adhesive, suitably conductive epoxy is used. The individual transducers are insulated from one another by a gap or space 8 between each. This gap 8extends slightly into faceplate 2 and prevents any wires in the faceplate from shorting together any of the individual transducers. The pressure release barrier 6 is a conductive syntactic foam. This is a material which has acoustically absorptive or deadening properties and is electrically conductive. Accordingly, the pressure release barrier provides an electrical path from the bottom side of each piezoelectric slab through to one or more wires 4 on the top of faceplate 2. The faceplate fiber wires provide the electrical path internally of tube body 3 where any voltages presented thereon are available for electron beam scanning or readout in the conventional manner. Not illustrated in this figure to complete a functional mosaic, a wax or paraffinlike substance is filled into the slits 8' or an electrically conductive thin foil material covers the top of the transducers. In the latter structure this directly places the entire top side of the individual transducers electrically in common. ln the first mentioned approach the common connection is made between the piezoelectric surfaces and the water. As is apparent, most water has sufficient electrical conductivity due to impurities for this application. If desired, the foil may be bonded to the transducer with conductive epoxy or ultrasonic welding techniques. In turn the foilis covered with a thin waterproof material. Alternatively, a thin rubber covering, either electrically conductive or with a thin electrically. conductive coating on its inner side, may be placed over the top of the transducer array and tube front to accomplish both functions of waterproofing the transducer andplacing the top side of the piezoelectric material 5 electrically in' common. In the wax approach, the wax maintains insulationbetween the individual transducers.

As has been described, the pressure release barrier 6 is a conductive syntactic foam. More particularly, this consists of a cured mixture of conductive epoxy resin and miniscule hollow glass balls. A magnified view of the material is illustrated at 9. A suitable conductive epoxy resin is manufactured by the Hysol Corporation of California and sold under the designation K-ZO." This is a two part epoxy in which silver has been added so that, in the cured form, the epoxy is electrically conductive. The other ingredient consists of miniscule hollow glass spheres, called Eccospheres." The size of the spheres in a given batch varies from about 0.0012 to 0.005 inches (30 to l25 microns) and are about Z-microns wall thickness. This variation is not important and either larger or smaller spheres as available may be used. Glass spheres as specified in this example are available from Emerson-Cummings Co, and are sold under the designation Eccospheres VT."

A layer of the conductive syntactic foam is manufactured as follows: Approximately parts by weight of the epoxy is thoroughly mixed with 1 part by weight of the glass spheres to form a uniform mixture. The mixture is then packed into a mold of the desired shape, taking care to ensure the filling of all corners in the mold, and allowed to cure on harden. The syntactic foam body is then removed from the mold. Suitably it is found that the foam can be ground, cut, and machined for finishing operations. Additionally, the specific gravity is less than one-it floats." In addition, the acoustic velocity in the foam substantially corresponds to that of water. Measurements made with an ordinary ohmmeter on the foam of a few tenths of an ohm irrespective of the electrode placement. While a very high conductivity is not a requisite or critical factor the cited results are very satisfactory. The slab or layer of material so formed and cut is at this stage represented as slab 10 in FlG. 2a.

'The slab of piezoelectric material 12 is suitably Lead Titanate-Lead Zirconate. This is available from Channel Industries under the designation CH 5400. Piezoelectric layer 12 is then attached to the surface of the syntactic foam slab 10 with a conductive adhesive material 13, suitably the conductive epoxy K-ZO, which provides both a firm mechanical bond and electrical continuity. The thickness of the slabs is a matter of design choice. By way of example the thickness of the piezoelectric layer is 0.012 inches and the thickness of the syntactic foam layer is 0.050 inches. Both may be of length and width of one inch.

As illustrated in FIG. 2b the assembled transducer is secured to the faceplate of a pickup-type imaging tube. A conductive adhesive 14 suitably epoxy K-20, is spread on either the remaining surface of the foam or the faceplate or both and the foam and faceplate are adhesively joined together. As previously described, faceplate 15 is of a conventional conductive fiber optic construction and consists, preferably, of 2-mi. electrically conductive wires 16 in 4-mil. centers in a glass or ceramic matrix. It is evident that the assembly described in the alternative may be completed by first securing same to the faceplate 15 before the faceplate is assembled to the imaging tube body.

The imaging tube as thus far formed with attached transducers is mounted in a suitable holding fixture. A saw, not illustrated, is then used to cut slots 18 through the, layers to obtain the structure of FIG. 3 and as was illustrated in FIG. 1. The grooves or slots 18 are cut through both horizontally and vertically to form a checkerboard or mosaic of independent ul trasonic transducers. The cut is preferably of a depth at 19 just sufficient to penetrate the fiber optic faceplate 15,. The saw used for cutting may be of tungsten carbide as thin as can be obtained. A 0.003-inch thick diamond saw is useful for this purpose.

The front end of the imaging tube is then covered with a thin waterproof rubber sheath 21 having a foil or other conductive coating on its inner surface which" places the upper surface of all the piezoelectric elements electrically in common.

Alternatively, instead of a sheath the slots 18 may be filled with a wax or paraffinlike substance 22 shown in FIG. 4. The wax maintains electrical insulation between individual transducers etc. in the mosaic when the imaging tube is submerged in water and the water, almost always containing some impurities, and therefore having sufficient electrical conductivity, acts as the electrical conductor common to the top surfaces of all the piezoelectric slabs. The elements in FIG. 4 similar to those in FIG. 3 are labeled with the same numerals primed. The wax may be added after the first parallel rows of slots are cut to provide mechanical support during cutting of the rows of slots perpendicular to the first. The wax is filled into these latter slots and then the upper surface of the piezoelectric is wiped clean.

It is apparent that an alternative transducer construction in which some of the rows or columns are electrically in common while being significantly decoupled or isolated acoustically, may be accomplished by simply cutting the slot separating those rows or columns toa depth nearly but not completely through the syntactic foam layer. I

As apparent, the transducer construction described in this application may be made of any size or shape, large or small, as is desired simply by cutting in the desired manner. Additionally, the materials described may be used as a single transducer without cutting. For example, the properties of the piezoelectric and syntactic foam pressure release barrier herein described are useful without an imaging tube and can be used in other combinations to detect ultrasonic energy in water. The acoustic properties of that combination closely approximate the acoustic impedance of water and therefore make such possible and desirable in other applications.

In operation an ultrasonic energy field is incident upon the sheath, not illustrated, covering the mosaic transducers of FIG. 1. As is conventional, the compressional wave energy distorts or compresses the piezoelectric 5 which in turn develops a voltage across its top and bottom faces proportional in magnitude to the applied stress. The voltages from the bottom surface of the individual transducer faces pass across the attached conductive syntactic foam material 6 to the wire fiber faceplate 2. Depending upon the number of wires 4 in the faceplate covered by the foam material, the voltages pass through faceplate 2 by means of wire or wires 4 to the inside evacuated regions of the imaging tube. The voltages so appearing are scanned or read" in the conventional manner by the electron beam. As is apparent, because of the groove spacing the transducers, they are isolated from one another both electrically and acoustically.

Should it be desired to replace the transducer mosaic attached to the imaging tube faceplate as illustrated in FIG. 1 with another having perhaps different thicknesses of piezoelectric or foam layers than the original substitution is relatively simple. The piezoelectric and syntactic foram layers being joined to the faceplate with epoxy are simply scrapped off and the faceplate is cleaned with a suitable epoxy solvent. Then a new mosaic is attached to the faceplate in the same manner as described for the bonding of the original. Likewise, the new material is cut with suitable grooves and of such spacing desired in the same manner described of the original.

It is to be understood that the above described arrangements are intended to be illustrative of the invention and not by way of limitation since numerous other arrangements and equivalents suggest themselves to those skilled in the art and do not depart from the spirit and scope of my invention. Accordingly, it is to be expressly understood that the invention is to be broadly construed within the spirit and scope of the appended claims.

What I claim is:

1. The method of manufacturing a transducer mosaic adapted for use in an image conversion tube which includes the steps of joining together in a sandwich like arrangement a layer of piezoelectric material; and a layer of electrically conductive syntactic foam material atop a fiber electronics faceplate, said faceplate having a plurality of substantially uniformly spaced and insulated conductive wires extending between the top and bottom surfaces thereof and slicing a plurality of slots through said piezoelectric and foam layers in at least two directions to form segments of said layers.

2. The method as defined in claim 1 wherein the step of slicing through said layers found comprises slicing a plurality of spaced slots in one direction and slicing a plurality of spaced slots perpendicular to the aforementioned slots to form a checkerboard mosaic.

3. The method as defined in claim 2 wherein the step of slicing through said piezoelectric and foam layers includes slicing to a depth sufiicient to just penetrate the surface of the fiber electronics faceplate.

4 The method of manufacturing an image conversion tube adapted to contain a mosaic of ultrasonic transducers comprising the steps of:

a. joining together with conductive epoxy material a slab of piezoelectric material with the front side of slab of electrically conductive syntactic foam material;

b. joining together with conductive epoxy material the back slotting therethrough a plurality of spaced parallel slots in one direction and a second spaced plurality of slots in a direction perpendicular to said first direction; each of said slots being of sufficient depth so as to extend through both said piezoelectric and syntactic foam slabs and sufficient to penetrate slightly the faceplate of said image conversion tube. 

2. The method as defined in claim 1 wherein the step of slicing through said layers found comprises slicing a plurality of spaced slots in one direction and slicing a plurality of spaced slots perpendicular to the aforementioned slots to form a checkerboard mosaic.
 3. The method as defined in claim 2 wherein the step of slicing through said piezoelectric and foam layers includes slicing to a depth sufficient to just penetrate the surface of the fiber electronics faceplate.
 4. The method of manufacturing an image conversion tube adapted to contain a mosaic of ultrasonic transducers comprising the steps of: a. joining together with conductive epoxy material a slab of piezoelectric material with the front side of slab of electrically conductive syntactic foam materiaL; b. joining together with conductive epoxy material the back side of said slab of foam material to a faceplate of an image conversion tube; said faceplate being of the type which contains a plurality of substantially uniformly spaced conductive wires insulated from one another which extend from the outside to the inside regions of said image conversion tube; c. slotting therethrough a plurality of spaced parallel slots in one direction and a second spaced plurality of slots in a direction perpendicular to said first direction; each of said slots being of sufficient depth so as to extend through both said piezoelectric and syntactic foam slabs and sufficient to penetrate slightly the faceplate of said image conversion tube. 